1. Field of the Invention
The present invention relates to semitrailers having frames adjustable in effective length to alter the spacing between locations on the ground to which the weight of the trailer and the load which it carries is applied.
2. Prior Art
Semitrailers have been used for transporting loads of various kinds, but the chassis of such semitrailers have been of fixed length so that the spacing between the forward connection of the semitrailer to a tractor and the rear wheel assembly of the trailer remains constant.
Because it has been necessary to maneuver semitrailers in close quarters for normal loading, the wheel base of such semitrailers has been made almost as short as possible. Consequently, the weight of the semitrailer and of its load has been transmitted to the ground at relatively close locations. Because of the proximity of the rear truck wheels and the rear semitrailer wheels, highway loads of semitrailers have been limited to a value below their actual carrying capacity. If the wheel assemblies are spaced farther apart to distribute the weight over a greater distance, the semitrailer is too long to maneuver easily in close quarters.
Another problem has arisen in connection with hauling dirt to fill depressions. Where a semitrailer having a dump body filled with dirt must be backed over soft, filled ground to dump its load for continuing to fill a depression, the traction of the rear wheel assembly of the tractor may be sufficiently poor so that either rotation of such wheels cannot propel the semitrailer backward to the brink of the fill, or the semitrailer must be backed with sufficient speed so that rotation of the tractor drive wheels will continue to move the semitrailer rearward to the brink. In the latter case the semitrailer may be driven at such speed and with such momentum that it cannot be stopped at the desired location without great danger of the rear wheel assembly of the semitrailer going over the brink of the fill. Under such circumstances the problem of positioning a semitrailer most advantageously for continuing a fill has been very difficult.